I'm struggling to see how these speeds are a direct consequence of certain phones being slower than others. My iPhone 6 happily consumes data at a rate of 100Mb

I'm struggling to see how these speeds are a direct consequence of certain phones being slower than others. My iPhone 6 happily consumes data at a rate of 100Mbps over 4G according to the Speedtest app. This phone must surely have an inferior modem and antennas compared to the much more modern devices mentioned in this article, yet on average they apparently perform much worse. Is the device itself really the only variable that could account for the difference? For example, I only get these speeds on my network, EE, because I pay for a "Max" plan which allows me to download data at the fastest speed possible. However, they sell cheaper plans with capped data rates. Perhaps in this scenario, iPhone users are choosing worse (cheaper) plans so they can afford an expensive phone?